A file has been created which can link Collaborative Perinatal Project data for women with relatives also in the Project. This has been imbedded in a file which classifies registrants by the number of Project pregnancies if they have no relatives registered. This larger file, has in turn, been merged with a file containing other genetic information, such as twin zygosity, and medical and psychological data for familial studies of malformations and other conditions. The record linkage file, as such, will not be changed unless experience in its use shows it to be erroneous or cumbersome.